1. Field of the Invention
The invention is directed to a method for manufacturing packets composed of linked sheet metal laminations for magnetic cores, known as sheet metal packets.
2. Description of the Prior Art
A method is disclosed in European Application 0 133 858 for manufacturing such sheet metal packets, laminations wherein are punched from a tape and are provided with depressions at one side and with elevations at the other side that coincide with the depressions and lie opposite them. In the form of at least two circular nipples these elevations are pressed into the depressions upon assembly of each packet. Instead of the depressions, cylindrical holes are punched into one lamination per sheet metal packet, this serving as parting lamella. The nipples of the neighboring laminations engage into these circular holes. The teachings of European Application are expressly incorporated herein by reference.
Among other things, sheet metal packets of this type are used in various electromagnetic apparatus such as, for example, inductors, transformers, actuating drives, actuators such as, for example, solenoid valves, etc.
The employment of sheet metal packets in magnetic circuits has been state of the art for many years and serves the purpose of reducing eddy currents that, for example, in transformers, contribute to an increase in the losses or, given solenoid valves, contribute to a lengthening of the switching times. As an alternative to sheet metal packets, toroidal tape cores are employed that, however, exhibit the disadvantage compared to sheet metal packets that the coils required for the drive must be slipped on before closing the magnetic circuit.
Due to the requirement of a rectangular iron cross section in sheet metal packets, in many instances the use of sheet metal packets cannot be optimized. In many applications, for example, it is desirable to keep the recesses for the sheet metal packets to be introduced round or, oval.
When a sheet metal packet having a rectangular iron cross section is then introduced into such a round or, oval recess, the comparatively low iron cross section relative to the diameter of the recess is disadvantageous. This disadvantage becomes particularly serious when the conditions of use require a miniaturization of the components, as is particularly necessary in internal combustion engines.
It is therefore an object of the present invention to provide a manufacturing method of the above type wherein sheet metal packets are also available that have a round or oval iron cross section.
This is inventively achieved by a method for manufacturing packets composed of linked sheet metal laminations for magnetic cores wherein laminations are punched from a tape and are provided with depressions at one side and are provided with projections at the other side that coincide with the depressions and lie opposite them, wherein the projections in the form of at least two circular nipples and are pressed into the depressions upon assembly of each packet, wherein cylindrical holes instead of the depressions are punched in one lamination per packet, this serving as separating a lamination, the nipples of the neighboring lamination engaging thereinto. Laminations are thereby punched from the band that respectively have different outside contours and are linked with one another to form a packet that at least partially has a round iron cross section. Accordingly, the sheet metal packet has graduated edges.
As a result of this measure, sheet metal packets can be fabricated that have their outside contour adapted to a round shape and whose iron cross section corresponds to the ideal circular shape to more than 95%.
Typically, laminations are thereby punched from the tape that have respectively different widths. These laminations of different widths are then linked to form a packet that has a nearly circular iron cross section.
In an alternative embodiment of the inventive method, E-shaped laminations are punched from the tape, their outside and/or middle leg exhibiting different widths. Due to the variation of the widths of the middle leg sheets, middle legs can be manufactured whose iron cross section nearly corresponds to the ideal circular shape. As a result, it is possible to slip circular coils onto the middle leg. Due to the variation of the widths of the outside leg sheets, the arising sheet metal packets can in turn be adapted to the circular or oval installation requirements.
An extremely high work output with only a single apparatus is achieved when the depressions and the nipples of each lamination are flow-coined with dies given simultaneous application of opposing force with counter-dies, whereby the nipple diameter is greater than that of the corresponding depression, and the nipple height is less than the depth of the corresponding depression, which has achieved at least 50% of the lamination thickness.
The depressions and the nipples are preferably flow-coined for at most another 10 ms by the dies after the counter-dies have reached their final position.
In an embodiment of the present invention, the nipple diameters are formed at most 20 xcexcm larger than the diameter of the corresponding depression, and the nipple height is formed at most 0.1 mm less than the depth of the corresponding depression.
Further, the laminations can be pre-coined or pre-punched at the rated locations of the depressions and the nipples.
The inventive apparatus for the implementation of the method has at least two dies and two counter-dies, that are height-adjustable in the matrix, in the coining station which produces the depressions and the nipples. Each counter-die is provided with a collar for defining its limit position at the support of the matrix; Braking elements are installed in the cut-out station of the finished lamination under the matrix, these braking elements proceeding transversely relative to the counter-die axes and exerting the required resistance in the joining of the individual, finished laminations to one another. Cutting dies that can be moved apart and moved into one another in turn in defined steps are located in the cut-out station. This setting of the cutting dies to different widths typically ensues automatically with an actuating drive.